Recently, the utilization of dispersed power system with smart grid, microgrid and new energy such as solar power and wind power is gathering attention, and further spread and expansion are expected. With this trend, the number of loads generating harmonics and the number of interconnected units of semiconductor power conversion systems are increasing, and hence there is concern over harmonics problem in the power distribution system. Since harmonics exert adverse influence on other interconnected devices, the harmonics are controlled and stipulated by harmonic guidelines etc. and various measures are taken to harmonics interference problem by using power active filters or other means.
However, conventional measures and methods might become insufficient from the viewpoint of harmonics compensation effect and control stability because the interconnection of many unspecified dispersed power sources everywhere could cause various problems such as increase of accumulated harmonics, complication of sources of harmonics, fluctuation of system impedance and load impedance with change in the construction of the distribution system, changeover of a phase advancing capacitor, and operating condition, and variation of system resonance characteristics.
As to the application and operation of active filters, adjusting operations are required to adjust control parameters on the spot and, moreover, operations are required for readjustment in case of change in the operating situation.
Based on the above-mentioned background, Patent Document 1 discloses a technique expanding a generalized periodic disturbance compensating method using the complex vector notation, proposed by the inventor of the present application et al., and correcting, by learning, the reciprocal of the transfer characteristic of the observer real system from information on complex vector loci of the periodic disturbance. The technique of Patent Document 1 is configured to extract a harmonic frequency component of each order in a power system active filter control system for controlling a system current as the object of control, automatically learning a frequency transfer function (taking account of dead times of sensors and control calculations and impedance characteristics collectively) from the harmonic suppressing command of each order to the sensed harmonic, and estimating and suppressing the current including the periodic disturbance in the form of harmonic. With this technique, it is possible to construct a robust power active filter control system eliminating the need for preparatory system identification.